Cobalt-based phosphide nano catalytic material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts, in particular to a cobalt-based phosphide nano catalytic material as well as a preparation method and application thereof. The preparation method comprises the following steps: dissolving a cobalt salt, urea and ammonium fluoride in water to obtain a mixed solution, placing a pretreated carbon cloth in the mixed solution, carrying out a hydrothermal reaction, taking out the carbon cloth to obtain a carbon cloth-loaded phosphating precursor, and carrying out hydrothermal reaction on the carbon cloth-loaded phosphating precursor in a protective atmosphere to obtain the carbon cloth-loaded phosphating precursor. Carrying out phosphating treatment with a phosphorus source; and carrying out constant piezoelectric deposition by taking the carbon cloth loaded cobalt phosphide as a working electrode and cobalt salt as an electrolyte to obtain the cobalt-based phosphide nano catalytic material. The cobalt-based phosphide nano catalytic material shows excellent catalytic activity, rapid reaction kinetics and good stability in HER, OER and full water splitting application, the preparation method is simple and controllable, the cobalt-based phosphide nano catalytic material is expected to replace a noble metal-based catalyst, and the cobalt-based phosphide nano catalytic material has a wide application prospect in the field of electro-catalysis energy conversion.

Description

A cobalt-based phosphide nanocatalytic material, its preparation method and its application Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a cobalt-based phosphide nanocatalytic material, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, as a zero-carbon energy carrier, has become an important component of the new energy system. Water electrolysis for hydrogen production is widely recognized as the core pathway for large-scale green hydrogen production. However, the kinetics of the oxygen evolution reaction (OER) at the anodic end and the hydrogen evolution reaction (HER) at the cathode are slow, with high energy barriers. Currently, noble metal-based catalysts such as RuO2 and IrO2 are the best catalysts for OER. However, due to their scarcity and high cost, they are difficult to apply to industrial production. Therefore, developing efficient, stable, and low-cost transition metal-based electrocatalysts has become a key challenge in realizing green hydrogen production.

[0003] Heterojunction catalysts are generally prepared by combining multiple components through physical composite or chemical synthesis processes. Utilizing heterostructure engineering technology, the structural disorder and defect sites at the interfaces between different components, resulting from lattice mismatch, are the core advantages that endow the catalysts with excellent physicochemical properties and enable highly efficient catalysis of specific reactions. Practice has shown that targeted modulation of the electronic structure of heterojunction interfaces can effectively optimize the adsorption and desorption processes of reaction intermediates, significantly improving the intrinsic activity of the catalyst. Simultaneously, the rich interfacial structure can enhance electron transport efficiency, ensuring the stability of the catalyst under long-term operating conditions and laying the foundation for its industrial application.

[0004] Metal phosphides have emerged as promising candidates for electrocatalysis of HER and OER in acid-base electrolytes due to their optimal conductivity and rapid charge transport. Nanostructured transition metal phosphides have become effective alternatives to noble metal-based electrocatalysts, exhibiting excellent physicochemical properties such as tunable composition, high conductivity, high current density, and sustained electrochemical durability in both acidic and alkaline solutions.

[0005] However, current metal phosphide materials have relatively weak interfacial electron transport capabilities, which is not conducive to electron transport at the three-phase interface.

[0006] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a cobalt-based phosphide nanocatalytic material, its preparation method and its application, in order to solve the problem of weak interfacial electron transport capability of existing metal phosphide materials.

[0008] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a cobalt-based phosphide nanocatalytic material, wherein the cobalt-based phosphide nanocatalytic material uses carbon cloth as a substrate, and crystalline cobalt phosphide and amorphous cobalt hydroxide are loaded on the substrate, and the amorphous cobalt hydroxide is distributed on the surface or interface of the crystalline cobalt phosphide; the preparation method includes the following steps: S1, cobalt salt, urea and ammonium fluoride are dissolved in water to obtain a mixed solution, pretreated carbon is arranged in the mixed solution, and after hydrothermal reaction, the carbon cloth is removed to obtain a carbon cloth-loaded phosphating precursor; S2, the carbon cloth-loaded phosphating precursor is subjected to phosphating treatment with a phosphorus source under a protective atmosphere to obtain carbon cloth-loaded cobalt phosphide; S3, the carbon cloth-loaded cobalt phosphide is used as a working electrode, and cobalt salt is used as an electrolyte to perform constant voltage electrodeposition to obtain the cobalt-based phosphide nanocatalytic material.

[0009] Optionally, in S1, the carbon cloth pretreatment includes the following steps: placing the carbon cloth in concentrated nitric acid and reacting it at 120-160℃ for 6-12 hours.

[0010] Optionally, in S1, the cobalt salt is cobalt nitrate hexahydrate or cobalt chloride.

[0011] Optionally, in S1, the hydrothermal reaction temperature is 120-160℃ and the time is 6-10h.

[0012] Optionally, in S1, the molar ratio of cobalt salt, urea and ammonium fluoride is 2: (4.5-5.5): (9.0-11.0).

[0013] Optionally, in S2, the phosphorus source is sodium hypophosphite or potassium hypophosphite, with 1.0g-2.0g of phosphorus source added per six square centimeters of carbon cloth.

[0014] Optionally, in S2, the process parameters of the phosphating treatment include at least one of the following: heating rate of 1-3℃ / min; phosphating temperature of 320-380℃; and holding time of 1.5-3h.

[0015] Optionally, in S3, the cobalt salt is cobalt nitrate hexahydrate or cobalt chloride; the concentration of the cobalt salt is 0.1 mol / L.

[0016] Optionally, in S3, during constant voltage electrodeposition, a carbon rod is used as the counter electrode and a silver chloride electrode is used as the reference electrode. The process parameters for constant voltage electrodeposition include: cathode voltage of -0.8V to -1.2V and time of 600-1200s.

[0017] Secondly, the present invention provides a cobalt-based phosphide nanocatalytic material, which uses carbon cloth as a substrate, on which crystalline cobalt phosphide and amorphous cobalt hydroxide are loaded, and the amorphous cobalt hydroxide is distributed in the form of nano islands on the surface or interface of crystalline cobalt phosphide; or it is prepared by the preparation method described above.

[0018] Thirdly, the present invention provides an application of a cobalt-based phosphide nanocatalyst as an electrocatalyst in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).

[0019] Beneficial Effects: This invention provides a cobalt-based phosphide nanocatalyst, its preparation method, and its applications. The cobalt-based phosphide nanocatalyst (CoP@amo-Co(OH)2@CC catalyst) provided by this invention exhibits excellent catalytic activity, rapid reaction kinetics, and good stability in HER, OER, and total water splitting applications. Furthermore, the preparation method is simple and controllable, and it holds promise as a replacement for noble metal-based catalysts, showing broad application prospects in the field of electrocatalytic energy conversion.

[0020] This catalyst exhibits excellent electrocatalytic performance for the hydrogen evolution reaction (HER): reaching 10 mA / cm². -2 The overpotential required for the current density is only 37 mV, significantly lower than that of the unmodified CoP@CC catalyst (88 mV), and comparable to that of the commercial Pt / C@CC catalyst (32 mV). The Tafel slope of this catalyst is 42 mVdec. -1 Slightly higher than commercial Pt / C@CC (38mVdec) -1 ), far lower than CoP@CC (95mVdec) -1 ( ), with faster HER reaction kinetics.

[0021] This catalyst exhibits excellent electrocatalytic performance for the oxygen evolution reaction (OER): at 10 mA / cm², it achieves high electrocatalytic performance. -2 The overpotential at current density is only 220 mV, which is superior to commercial IrO2@CC catalysts. The Tafel slope is as low as 55 mVdec. -1 The lowest charge transfer resistance further confirms its rapid OER reaction kinetics. The Faraday efficiency reaches 98.28%, and its performance showed no significant decline after 90 hours of stability testing, demonstrating excellent OER stability.

[0022] This catalyst exhibits a larger electrochemical active surface area and abundant active sites: in the HER test system, the Cdl value is 86.17 mFcm. -2 Higher than CoP@CC (65.71mFcm) -2 In the OER testing system, the Cdl value reached as high as 94.75 mFcm. -2It was significantly higher than that of CoP@CC (49.98 mFcm). -2 ) and commercial IrO2@CC (36.44mFcm) -2 ).

[0023] This catalyst exhibits excellent overall water splitting performance: at 10 mA / cm²... -2 When used simultaneously as both cathode and anode in a complete water splitting device, the electrolysis voltage is as low as 1.49V, lower than that of commercially available Pt / C@CC||RuO2@CC (1.66V). Furthermore, the complete water splitting device can operate at 10mAcm... -2 The performance degradation was negligible after 50 hours of stable operation under current density testing, demonstrating good prospects for practical applications. Attached Figure Description

[0024] Figure 1 is a schematic diagram of the process for preparing cobalt-based phosphide nanocatalytic materials according to an embodiment of the present invention.

[0025] Figure 2 is a flowchart of the preparation of cobalt-based phosphide nanocatalytic materials according to an embodiment of the present invention.

[0026] Figure 3 shows a comparison of the morphology of different catalysts.

[0027] Figure 4 shows the electronic structure diagrams of different catalysts.

[0028] Figure 5. Comparison of the electrochemical properties of hydrogen evolution reaction with different catalysts.

[0029] Figure 6 shows a comparison of the electric double-layer capacitance of the hydrogen evolution reaction with different catalysts.

[0030] Figure 7 is a comparison of the electrochemical properties of the oxygen evolution reaction with different catalysts.

[0031] Figure 8. Comparison of double-layer capacitance tests for oxygen evolution reaction with different catalysts.

[0032] Figure 9. Comparison of the properties of water electrolysis with different catalysts. Detailed Implementation

[0033] This invention provides a cobalt-based phosphide nanocatalytic material, its preparation method, and its applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0034] While existing cobalt-based phosphide electrocatalysts have shown some potential in water electrolysis applications, the following specific technical defects still limit the improvement of their actual catalytic performance: (I) Insufficient active sites due to single crystal phase structure: Existing cobalt-based phosphides (such as CoP) mostly exist in a single crystal state, and their surface active sites are mainly limited to specific crystal faces, resulting in a single type and limited number of active sites. During the electrocatalytic reaction, the adsorption configuration of reaction intermediates is restricted, making it difficult to simultaneously optimize the multi-step reaction pathways of HER and OER, leading to poor bifunctional catalytic performance.

[0035] (ii) Difficulty in controlling the electronic structure of the interface: Although the heterojunction strategy has been proven to optimize electron transport, the construction of existing cobalt-based phosphide heterojunctions mostly relies on complex multi-step synthesis or high-temperature treatment, resulting in weak interfacial contact and weak electronic coupling between heterojunctions, making it difficult to achieve effective charge redistribution. This leads to limited improvement in the intrinsic activity of the catalyst and insufficient optimization of the adsorption free energy of reaction intermediates.

[0036] (iii) Limited electrochemical active area: Conventional cobalt-based phosphide materials have limited specific surface area and lack effective surface defect engineering, resulting in an insufficient number of exposed active sites. In alkaline electrolytes, mass transport is limited, and the contact between the catalyst and the electrolyte is insufficient, making it difficult to increase the current density and meet the industrial application requirements at high current densities.

[0037] (iv) Poor long-term operational stability: Under alkaline water electrolysis conditions, existing cobalt-based phosphide materials are prone to surface oxidation, structural collapse, or dissolution of active components, leading to a gradual decline in catalytic performance over time. In particular, heterogeneous structures with weak interfacial bonding are prone to component stripping under high potential or high current density, further exacerbating stability issues.

[0038] (v) Lack of targeted interface engineering strategies: Although heterojunction catalysts have been extensively studied, there are currently no systematic research reports on the construction of crystalline / amorphous heterojunctions between cobalt-based phosphides and cobalt-based hydroxides and their synergistic catalytic mechanisms. How to induce the in-situ formation of amorphous cobalt hydroxide nanoislands on the surface of cobalt-based phosphides through controllable electrochemical means and achieve targeted regulation of the interface electronic structure remains a technological gap in this field.

[0039] Based on this, this embodiment provides a method for preparing cobalt-based phosphide nanocatalytic materials. The cobalt-based phosphide nanocatalytic materials use carbon cloth (denoted as CC) as a substrate, on which crystalline cobalt phosphide (denoted as CoP) and amorphous cobalt hydroxide (denoted as amo-Co(OH)2) are loaded, and the amorphous cobalt hydroxide is distributed on the surface or interface of the crystalline cobalt phosphide. The preparation method, as shown in Figure 1, includes the following steps: S1, cobalt salt, urea, and ammonium fluoride are dissolved in water to obtain a mixed solution; the pretreated carbon cloth... After hydrothermal reaction in the mixed solution, the carbon cloth is removed to obtain a carbon cloth-supported phosphating precursor, denoted as Co(OH)F@CC; S2, the carbon cloth-supported phosphating precursor is phosphated with a phosphorus source under a protective atmosphere to obtain carbon cloth-supported cobalt phosphide, denoted as CoP@CC; S3, the carbon cloth-supported cobalt phosphide is used as the working electrode, and cobalt salt is used as the electrolyte for constant voltage electrodeposition to obtain the cobalt-based phosphide nanocatalytic material, denoted as CoP@amo-Co(OH)2@CC.

[0040] In this embodiment, the cobalt salt provides Co. 2+ Ammonium fluoride provides F - Urea provides mild OH- - F - Co 2+ OH - The three components coordinate to form a layered Co(OH)F structure. Carbon cloth serves as the catalyst substrate, providing a conductive network to ensure the conductivity and mechanical flexibility of the cobalt-based phosphide nanocatalyst material. Surface hydroxyl / carboxyl defects provide nucleation sites for Co(OH)F, achieving uniform loading of the precursor. Alternatively, carbon fiber paper can be used. As shown in Figure 2, the Co(OH)F@CC obtained in S1 serves as the phosphating precursor, providing a Co source and substrate loading sites for CoP. Its layered nanostructure is completely preserved after phosphating, transforming into a highly active CoP phase, and surface defects provide ample sites for the phosphating reaction. The cobalt salt in S3 provides Co for the electrodeposition reaction. 2+ Electrodeposition is performed under constant voltage conditions, reacting with OH in the solution. - Amorphous Co(OH)₂ is generated and uniformly loaded onto the surface of CoP@CC. The catalytic performance and structural stability of the final cobalt-based phosphide nanocatalyst CoP@amo-Co(OH)₂@CC depend primarily on: the uniformity and loading of the nanomorphology of the Co(OH)F precursor, the phosphating conversion rate and crystal integrity of cobalt phosphide, and the amorphous structure, loading, and uniform coating of Co(OH)₂.

[0041] The cobalt-based phosphide nanocatalyst material (CoP@amo-Co(OH)2@CC catalyst) obtained in this embodiment exhibits excellent catalytic activity, rapid reaction kinetics, and good stability in HER, OER, and total water splitting applications. Moreover, the preparation method is simple and controllable, and it is expected to replace noble metal-based catalysts, showing broad application prospects in the field of electrocatalytic energy conversion.

[0042] This catalyst exhibits excellent electrocatalytic performance for the hydrogen evolution reaction (HER): reaching 10 mA / cm². -2 The overpotential required for the current density is only 37 mV, significantly lower than that of the unmodified CoP@CC catalyst (88 mV), and comparable to that of the commercial Pt / C@CC catalyst (32 mV). The Tafel slope of this catalyst is 42 mVdec. -1， Slightly higher than commercial Pt / C@CC (38mVdec) -1 ), far lower than CoP@CC (95mVdec) -1 It has faster HER reaction kinetics.

[0043] This catalyst exhibits excellent electrocatalytic performance for the oxygen evolution reaction (OER): at 10 mA / cm², it achieves high electrocatalytic performance. -2 The overpotential at current density is only 220 mV, which is superior to commercial IrO2@CC catalysts. The Tafel slope is as low as 55 mVdec. -1 The lowest charge transfer resistance further confirms its rapid OER reaction kinetics. The Faraday efficiency reaches 98.28%, and its performance showed no significant decline after 90 hours of stability testing, demonstrating excellent OER stability.

[0044] This catalyst exhibits a larger electrochemical active surface area and abundant active sites: in the HER test system, the Cdl value is 86.17 mFcm. -2 Higher than CoP@CC (65.71mFcm) -2 In the OER testing system, the Cdl value reached as high as 94.75 mFcm. -2 It was significantly higher than that of CoP@CC (49.98 mFcm). -2 ) and commercial IrO2@CC (36.44mFcm) -2 ).

[0045] This catalyst exhibits excellent overall water splitting performance: at 10 mA / cm²... -2 When used simultaneously as both cathode and anode in a complete water splitting device, the electrolysis voltage is as low as 1.49V, lower than that of commercially available Pt / C@CC||RuO2@CC (1.66V). Furthermore, the complete water splitting device can operate at 10mAcm... -2The performance degradation was negligible after 50 hours of stable operation under current density testing, demonstrating good prospects for practical applications.

[0046] In some embodiments, the carbon cloth pretreatment includes the following steps: placing the carbon cloth in concentrated nitric acid and reacting it at 120-160°C for 6-12 hours.

[0047] Of course, the carbon cloth treated with concentrated nitric acid in this embodiment still needs to be washed. Specifically, it may include: taking it out and washing the carbon cloth with deionized water until it is neutral, then placing it in acetone and sonicating for 10 minutes to remove the grease on the surface of the carbon cloth, then washing it three times with ethanol, washing it three times with deionized water, and then drying it for later use.

[0048] In some embodiments, the cobalt nitrate hexahydrate or cobalt chloride is used.

[0049] In some implementations, the hydrothermal reaction is carried out at a temperature of 120-160°C for 6-10 hours.

[0050] It should be noted that in this embodiment, both the temperature and time of the hydrothermal reaction jointly determine the crystal development and nano-morphology of Co(OH)F, which are key to the quality of the precursor: Too low a temperature results in a slow urea hydrolysis rate and reduced OH... - Insufficient release, Co 2+ Incomplete coordination leads to the formation of amorphous precursor Co(OH)F; excessively high temperature causes urea hydrolysis to be too rapid, resulting in localized OH- - A sudden increase in concentration leads to the formation of the Co(OH)2 impurity phase, and excessively rapid grain growth results in large particle agglomeration and a decrease in specific surface area. If the time is too short, the crystal form is not fully developed, the precursor is microcrystalline, and the loading is low. If the time is too long, the grains grow excessively, the nano-morphology collapses, the specific surface area decreases, and the number of active sites of CoP decreases after subsequent phosphating.

[0051] In some embodiments, the molar ratio of cobalt salt, urea and ammonium fluoride is 2: (4.5-5.5): (9.0-11.0), such as 2:5:10, 2:4.5:9, 2:5.5:11.

[0052] In some embodiments, the phosphorus source is sodium hypophosphite or potassium hypophosphite, with 1.0-2.0 g of phosphorus source added per six square centimeters of carbon cloth.

[0053] It should be noted that in this embodiment, sodium hypophosphite or potassium hypophosphite is used as the core phosphorus source for phosphating. Under a protective gas atmosphere such as nitrogen, it decomposes at 350°C and reacts with Co in Co(OH)F, completely converting it to CoP. A suitable mass ratio of sodium hypophosphite to Co(OH)F@CC should be used, as this ratio determines the phosphating conversion rate: insufficient sodium hypophosphite results in incomplete phosphating of Co(OH)F, low cobalt phosphide activity, and decreased conductivity and catalytic activity; excessive sodium hypophosphite leads to over-phosphating of CoP, generating impurity phases and corroding the carbon cloth surface, damaging the experimental substrate.

[0054] In some embodiments, the process parameters of the phosphating treatment include at least one of the following: a heating rate of 1-3℃ / min, such as 1℃ / min, 2℃ / min, or 3℃ / min; a phosphating temperature of 320-380℃, such as 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, or 380℃; and a holding time of 1.5-3h, such as 1.5h, 2h, 2.5h, or 3h.

[0055] It should be noted that the appropriate phosphating process parameters directly determine the crystal form, phosphating uniformity, and bonding strength with carbon cloth of CoP, which is the core of active phase formation: Too rapid a heating rate: Sodium hypophosphite decomposes rapidly, leading to localized over-phosphating, and Co(OH)F decomposes rapidly, causing a sudden volume change that reduces the bonding strength between the active phase and carbon cloth, making it prone to detachment; Too low a calcination temperature: Sodium hypophosphite cannot decompose, the phosphating reaction cannot occur, and CoP cannot be generated; Too high a calcination temperature: CoP crystals grow, reducing the specific surface area; Too short a holding time: The phosphating reaction is insufficient, Co(OH)F remains, and the CoP conversion rate is low; Too long a holding time: CoP grains grow excessively, reducing active sites, and long-term corrosion of carbon cloth reduces the mechanical strength of the substrate.

[0056] Of course, during the phosphating process, the exhaust gas is collected throughout using copper sulfate solution to avoid environmental pollution, and after natural cooling, the toxic exhaust gas produced during phosphating is efficiently absorbed and converted into a solid through a precipitation reaction, preventing the escape of toxic exhaust gas from polluting the environment and harming laboratory personnel. Alternatives include copper nitrate solution and copper acetate solution.

[0057] In some embodiments, in S3, the cobalt salt is cobalt nitrate hexahydrate or cobalt chloride; the concentration of the cobalt salt is 0.05-0.15 mol / L, such as 0.05 mol / L, 0.1 mol / L, or 0.15 mol / L.

[0058] In this embodiment, the concentration of the cobalt nitrate solution is 0.1 mol / L. The concentration determines the loading and deposition structure of amorphous Co(OH)₂: Too high a concentration results in Co… 2+Excessive migration rate leads to excessively high cathode reduction rate and excessive amorphous Co(OH)2 loading, resulting in thick-layer agglomeration that blocks the active sites of CoP; insufficient concentration leads to Co... 2+ When the concentration is low and the deposition amount is too small, a complete coating layer cannot be formed, and the synergistic catalytic effect of CoP and amorphous Co(OH)2 is weak.

[0059] In some embodiments, during constant voltage electrodeposition in S3, a carbon rod is used as the counter electrode and a silver chloride electrode is used as the reference electrode. The process parameters for constant voltage electrodeposition include: a cathode voltage of -0.8V to -1.2V and a time of 600-1200s.

[0060] It should be noted that the cathode voltage and deposition time during the electrodeposition stage determine the phase structure (amorphous / crystalline), loading, and coating uniformity of amorphous Co(OH)2, and are crucial for the formation of the core-shell structure: Too high a voltage results in an excessively fast cathode reduction rate, leading to Co... 2+ Rapid reduction produces crystalline Co(OH)₂, losing the high reactivity of the amorphous structure, and the deposited layer is thick and loose, easily detached; simultaneously, the hydrogen evolution reaction intensifies, pores appear in the deposited layer, and the structure is not dense; insufficient voltage: Co 2+ Insufficient reduction driving force results in almost no deposition, making it impossible to form an amorphous Co(OH)2 coating layer. Too short a deposition time leads to insufficient deposition, incomplete coating, exposed CoP, and weak synergistic catalytic effect. Too long a deposition time results in excessive deposition, an overly thick amorphous Co(OH)2 layer, blocking CoP active sites and causing the amorphous structure to transform into a crystalline form, leading to performance degradation. It should also be noted that after constant voltage electrodeposition, the obtained sample needs to be repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 60℃ for 6 hours. The drying temperature (60℃) affects the bonding force between the active phase and the carbon cloth, and the stability of the amorphous structure. If the drying temperature is too high, the hydrothermal product Co(OH)F easily dehydrates to form impurities, the electrodeposited amorphous Co(OH)2 easily crystallizes, and rapid water evaporation leads to nanoparticle aggregation. Failure to vacuum dry after electrodeposition results in the sample surface being in contact with air during atmospheric pressure drying, causing slight oxidation of the amorphous Co(OH)2 and damage to the amorphous structure.

[0061] This embodiment also provides a cobalt-based phosphide nanocatalytic material, using carbon cloth (denoted as CC) as a substrate, on which crystalline cobalt phosphide (denoted as CoP) and amorphous cobalt hydroxide (denoted as amo-Co(OH)2) are loaded, and the amorphous cobalt hydroxide is distributed in the form of nano islands on the surface or interface of crystalline cobalt phosphide (forming a heterojunction structure); or it is prepared by the preparation method described above.

[0062] The cobalt-based phosphide nanocatalyst material (CoP@amo-Co(OH)2@CC catalyst) obtained in this embodiment exhibits excellent catalytic activity, rapid reaction kinetics, and good stability in HER, OER, and total water splitting applications. Moreover, the preparation method is simple and controllable, and it is expected to replace noble metal-based catalysts, showing broad application prospects in the field of electrocatalytic energy conversion.

[0063] This embodiment also provides the application of cobalt-based phosphide nanocatalysts as electrocatalysts in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).

[0064] Because the CoP@amo-Co(OH)2@CC catalyst obtained in this embodiment has excellent bifunctional activity (including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)), it can be applied to both HER and OER. Furthermore, it can be used simultaneously as both cathode and anode in water electrolysis devices.

[0065] The present invention will be further described below through specific embodiments.

[0066] Example 1: A method for preparing a cobalt-based phosphide nanocatalytic material, comprising the following steps: 1. Pretreatment of carbon cloth: 2×3cm 2 The carbon cloth was placed in a polytetrafluoroethylene reactor containing 20 mL of concentrated nitric acid and reacted at 140 °C for 10 h. After that, the carbon cloth was taken out and washed with deionized water until neutral. Then it was placed in acetone and sonicated for 10 min to remove the grease on the surface of the carbon cloth. Then it was washed with ethanol 3 times and deionized water 3 times before being dried for later use.

[0067] 2. Synthesis of Co(OH)F@CC: 0.582 g (2 mmol) cobalt nitrate hexahydrate, 0.185 g (5 mmol) ammonium fluoride, and 0.601 g (10 mmol) urea were dissolved in 40 mL of deionized water and stirred for 30 min. The solution was then transferred to a polytetrafluoroethylene reactor, and a 2×3 cm pre-treated carbon cloth was placed inside. 2 Carbon cloth was subjected to a hydrothermal reaction at 140℃ for 8 hours. The carbon cloth was then removed and washed three times with deionized water and three times with anhydrous ethanol. It was then dried at 60℃ to obtain the carbon cloth-supported phosphating precursor Co(OH)F@CC.

[0068] 3. Synthesis of CoP@amo-Co(OH)2@CC: 1.5g of sodium hypophosphite and the prepared Co(OH)F@CC were placed at opposite ends of a ceramic boat and placed in a sealed tube furnace. The end containing the sodium hypophosphite was positioned upstream of the furnace. Phosphating was carried out under a nitrogen atmosphere via chemical vapor deposition, with the temperature increased from room temperature to 350℃ at a rate of 2℃ / min. -1The mixture was kept at this temperature for 2 hours, and the exhaust gas was collected throughout the process using copper sulfate solution to avoid environmental pollution. After natural cooling, cobalt phosphide CoP@CC loaded on carbon cloth was obtained.

[0069] 4. Dissolve 1.455 g (5 mmol) of cobalt nitrate hexahydrate in 50 mL of deionized water and stir on a magnetic stirrer for 30 min to obtain the electrolyte. Use CoP@CC as the working electrode, a carbon rod as the counter electrode, and a silver chloride electrode as the reference electrode for constant voltage electrodeposition. Perform iterative electrodeposition at a cathode voltage of -1.0 V for 800 s, remove the sample, rinse repeatedly with deionized water, and then dry in a vacuum drying oven at 60 °C for 6 h to obtain the cobalt-based phosphide nanocatalyst material CoP@amo-Co(OH)2@CC.

[0070] The following characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), systematically analyze the physicochemical properties of the catalytic materials obtained in this embodiment, such as crystal structure, morphology, size distribution, and microstructure. Electrochemical testing methods, including linear sweep voltammetry, chronoamperometry, and AC impedance spectroscopy, comprehensively evaluate the water electrolysis catalytic activity, long-term stability, and reaction kinetics of the catalytic materials obtained in this embodiment. Specific characterization results are as follows: The microstructures of CoP@CC obtained in step 3 and CoP@amo-Co(OH)2@CC obtained in step 4 of this embodiment were observed using SEM, and the results are shown in Figure 3. As shown in Figure 3a, the carbon cloth-supported cobalt phosphide CoP@CC exhibits a nanoflower-like structure. The morphology of CoP@amo-Co(OH)2@CC obtained after electrodeposition is shown in Figures 3b and 3c, maintaining the intact nanoflower-like morphology, except for the addition of some stacked lamellar structures on the surface. These stacked lamellar structures increase the specific surface area, thereby increasing the surface active sites and promoting the occurrence of electrocatalytic reactions. Further analysis of its structure was conducted using high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED). As shown in Figure 3e, the successful construction of the amorphous and crystalline heterogeneous interface was clearly observed. No obvious lattice fringes were observed in Figure 3d, indicating the successful construction of the amorphous state and exposing the (112) crystal plane of CoP with a lattice spacing of 0.196 nm. Further verification was made using the selected area electron diffraction pattern of the corresponding region, as shown in Figure 3h. The electron diffraction pattern in this region corresponds to the (111), (112), and (221) crystal planes of CoP. These test results demonstrate the successful synthesis of the CoP@amo-Co(OH)2@CC electrocatalytic composite material. Figures 3j-m show the elemental surface scans, indicating a uniform distribution of Co, O, and P elements. Based on the surface scan image of element P, it can be concluded that the outer electroplated stacked sheet structure is Co(OH)2, while the inner layer is a CoP structure. These results further prove the successful construction of the heterogeneous interface.

[0071] The surface chemical state and electronic structure of CoP@CC obtained in step 3 and CoP@amo-Co(OH)2@CC obtained in step 4 of this embodiment were analyzed by XPS, and the results are shown in Figure 4. In Figure 4a, the powder diffraction patterns of CoP@CC and CoP@amo-Co(OH)2@CC are shown. The XPS results of CoP@CC and CoP@amo-Co(OH)2@CC are shown in Figure 4b. The XPS full spectrum in Figure 4b confirms the presence of Co, C, P, and O elements in the catalyst. The high-resolution spectrum of Co 2p is shown in Figure 4c; the characteristic peaks at 803.1 eV and 787.5 eV are satellite peaks of Co, and the characteristic peaks at 800.1 eV and 783.1 eV correspond to Co. 2+ The peaks near 796.8 eV and 783.1 eV correspond to the Co 2p of CoP@amo-Co(OH)2@CC, respectively. 1 / 2 and Co2p 3 / 2 Compared to CoP@CC, the Co-P peaks at 793.5 eV and 778.7 eV disappeared. This is due to the obscuring of the XPS signal by a relatively thick layer of amorphous cobalt hydroxide plated on the outer layer. And compared to CoP@CC, the Co 2p peaks... 1 / 2 The characteristic peak of Co 2p showed a positive shift of 0.9 eV. 3 / 2 The characteristic peak shifted positively by 1.0 eV, indicating that CoP@amo-Co(OH)2@CC has greater electron transfer efficiency. The fine spectrum of O 1s shows that both CoP@CC and CoP@amo-Co(OH)2@CC samples contain adsorbed oxygen species (532.7 eV) and surface-adsorbed hydroxyl species at 531.2 eV. Simultaneously, due to the electroplating of a layer of Co(OH)2 on the surface of the CoP sample, a new metal-O bond characteristic peak at 530.5 eV appears in CoP@amo-Co(OH)2@CC. The high-resolution spectrum of P 2p is shown in Figure 3e, indicating the presence of PO bonds (133.3 eV) and 2p bonds in CoP@CC. 1 / 2 (130.5 eV) and 2p 3 / 2 The characteristic peak is 129.5 eV. However, due to the shielding effect of surface Co(OH)2 on the XPS signal, the 2p peak in CoP@amo-Co(OH)2@CC is affected. 1 / 2 and 2p 3 / 2The characteristic peaks disappeared. Ultraviolet photoelectron spectroscopy (UPS) calculations revealed the d-band centers of CoP@CC and CoP@amo-Co(OH)2@CC. The d-band center of CoP@amo-Co(OH)2@CC was located at -4.93 eV, which is closer to the Fermi level than that of CoP@CC (-5.28 eV). According to the d-band center theory, the relative position of the d-band center to the Fermi level of a transition metal catalyst affects its surface adsorption energy. A d-band center closer to the Fermi level can enhance the adsorption of active sites and reaction intermediates, thereby lowering the reaction energy barrier and improving intrinsic catalytic activity. Therefore, the introduction of the amorphous Co(OH)2 structure modulates the d-band electron distribution of CoP, thus enhancing the electrochemical performance of HER.

[0072] The hydrogen evolution reaction (HER) performance of different catalysts in 1.0 M KOH solution was measured using a three-electrode system, as shown in Figure 5. The linear sweep voltammetry (LSV) curves (Figure 5a) indicate that the electrodeposited catalyst CoP@amo-Co(OH)2@CC exhibits the best HER performance compared to CoP@CC, requiring only a 37 mV overpotential to reach 10 mV cm⁻¹. -2 The current density is significantly lower than that of CoP@CC (current density is 88mV cm⁻¹). -2 It is comparable to commercially available catalyst Pt / C@CC (current density 32 mV / cm). -2 This further validated its excellent HER activity and its broad range of potential alternative commercial catalysts.

[0073] The reaction kinetics of the catalyst were further studied using the Tafel slope: as shown in Figure 5b, CoP@amo-Co(OH)2@CC (42mV dec -1 The Tafel slope of the catalyst is slightly higher than that of the commercially available catalyst Pt / C@CC (38mV dec). -1 ), far lower than CoP@CC (95mV dec -1 Therefore, compared with CoP@CC, the catalyst CoP@amo-Co(OH)2@CC obtained in this embodiment has faster HER reaction kinetics.

[0074] In addition, electrochemical impedance spectroscopy (EIS) was measured to gain a deeper understanding of the electron transfer kinetics of HER. Figure 5c shows the impedance spectra of different catalysts. It can be seen that compared with CoP@CC, CoP@amo-Co(OH)2@CC has a smaller impedance ring, indicating that CoP@amo-Co(OH)2@CC containing heterojunction has lower charge transfer resistance, better conductivity, and faster reaction kinetics. As shown in Figure 5d, the Faradaic efficiency of the prepared catalyst is 99.08%. The electrochemical stability of CoP@amo-Co(OH)2@CC is shown in Figures 5e and 5f. The LSV curve after 1000 CV cycles showed almost no change, and the chronoamperometry stability test after 80 hours showed almost no decay, indicating that CoP@amo-Co(OH)2@CC has good HER stability.

[0075] This embodiment operates within a voltage range of 0.12-0.22V vs. RHE, and 10-60mV s. -1 The double-layer capacitance of the electrocatalytic materials was tested at a scanning rate of [missing value] to investigate the electrochemical activity of different electrocatalytic materials. Subsequently, the Cdl value was calculated by fitting the cyclic voltammetry curves to evaluate this key parameter closely related to the number of exposed active sites. The results are shown in Figure 6. It can be seen that the Cdl of CoP@amo-Co(OH)2@CC is 86.17 mF cm⁻¹. -2 , greater than CoP@CC (65.71mF cm -2 ), and commercial Pt / C@CC (95.24mF cm), -2 The results are comparable. Compared to CoP@CC, the CoP@amo-Co(OH)2@CC heterojunction has a larger electrochemical active area and more active sites in electrocatalytic reactions, which is beneficial for HER.

[0076] The oxygen evolution response (OER) performance of different catalysts in 1.0 M KOH solution was tested using a three-electrode system, and the results are shown in Figure 7. The LSV curve shown in Figure 7a indicates that, compared to CoP@CC, the CoP@amo-Co(OH)2@CC catalyst exhibits the best OER performance at 10 mA cm⁻¹. -2 The overpotential at this point is only 220 mV, which is superior to that of commercial IrO2@CC catalysts. Furthermore, as shown in Figure 7b, the Tafel slope of CoP@amo-Co(OH)2@CC is the lowest at 55 mV. -1The OER reaction kinetics are the fastest. As shown in Figure 7c (electrochemical impedance spectroscopy), the CoP@amo-Co(OH)2@CC catalyst exhibits the lowest impedance, further indicating its faster charge transfer rate and reaction kinetics. Furthermore, Figure 7d shows that the CoP@amo-Co(OH)2@CC catalyst has a Faradaic efficiency of 98.28%. The electrochemical stability of CoP@amo-Co(OH)2@CC is shown in Figures 7e and 7f; the LSV curves show almost no change before and after 1000 CV cycles, and the efficiency at 10 mA cm⁻¹ remains relatively stable. -2 The current density did not decrease significantly after 90 hours of testing, indicating that CoP@amo-Co(OH)2@CC has good OER stability.

[0077] In this embodiment, the double-layer capacitance fitted by cyclic voltammetry was used to evaluate the electrochemical active area of ​​the obtained catalyst, in order to explore the electrochemical activity of different electrocatalytic materials. The results are shown in Figure 8: the Cdl value of CoP@amo-Co(OH)2@CC is 94.75 mF cm⁻¹. -2 , greater than CoP@CC (49.98mFcm) -2 ), and higher than commercial IrO2@CC (36.44 mFcm). -2 Compared to CoP@CC, the CoP@amo-Co(OH)2@CC heterojunction has a larger active area, which can provide more active sites and significantly improve OER activity.

[0078] Because the CoP@amo-Co(OH)2@CC catalyst obtained in this embodiment exhibits excellent bifunctional activity, it can be used simultaneously as both a cathode and anode in an electrolytic water device. As shown in Figure 9a, at 10 mA cm⁻¹ -2 The electrolysis voltage of the CoP@amo-Co(OH)2@CC||CoP@amo-Co(OH)2@CC electrode is as low as 1.49V, lower than that of the commercially available Pt / C@CC||RuO2@CC (1.66V). Furthermore, as shown in Figure 9b, the total water splitting device can operate at 10mA cm⁻¹. -2 The performance degradation was negligible after 50 hours of stable operation under current density testing.

[0079] In summary, this invention provides a cobalt-based phosphide nanocatalytic material, its preparation method, and its applications. The cobalt-based phosphide nanocatalytic material (CoP@amo-Co(OH)2@CC catalyst) provided by this invention exhibits excellent catalytic activity, rapid reaction kinetics, and good stability in HER, OER, and total water splitting applications. Furthermore, the preparation method is simple and controllable, and it holds promise as a replacement for noble metal-based catalysts, showing broad application prospects in the field of electrocatalytic energy conversion.

[0080] This catalyst exhibits excellent electrocatalytic performance for the hydrogen evolution reaction (HER): reaching 10 mA / cm². -2 The overpotential required for the current density is only 37 mV, significantly lower than that of the unmodified CoP@CC catalyst (88 mV), and comparable to that of the commercial Pt / C@CC catalyst (32 mV). The Tafel slope of this catalyst is 42 mVdec. -1， Slightly higher than commercial Pt / C@CC (38mVdec) -1 ), far lower than CoP@CC (95mVdec) -1 It has faster HER reaction kinetics.

[0081] This catalyst exhibits excellent electrocatalytic performance for the oxygen evolution reaction (OER): at 10 mA / cm², it achieves high electrocatalytic performance. -2 The overpotential at current density is only 220 mV, which is superior to commercial IrO2@CC catalysts. The Tafel slope is as low as 55 mVdec. -1 The lowest charge transfer resistance further confirms its rapid OER reaction kinetics. The Faraday efficiency reaches 98.28%, and its performance showed no significant decline after 90 hours of stability testing, demonstrating excellent OER stability.

[0082] This catalyst exhibits a larger electrochemical active surface area and abundant active sites: in the HER test system, the Cdl value is 86.17 mFcm. -2 Higher than CoP@CC (65.71mFcm) -2 In the OER testing system, the Cdl value reached as high as 94.75 mFcm. -2 It was significantly higher than that of CoP@CC (49.98 mFcm). -2 ) and commercial IrO2@CC (36.44mFcm) -2 ).

[0083] This catalyst exhibits excellent overall water splitting performance: at 10 mA / cm²... -2 When used simultaneously as both cathode and anode in a complete water splitting device, the electrolysis voltage is as low as 1.49V, lower than that of commercially available Pt / C@CC||RuO2@CC (1.66V). Furthermore, the complete water splitting device can operate at 10mAcm... -2 The performance degradation was negligible after 50 hours of stable operation under current density testing, demonstrating good prospects for practical applications.

[0084] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a cobalt-based phosphide nanocatalytic material, characterized in that, The cobalt-based phosphide nanocatalyst material uses carbon cloth as a substrate, on which crystalline cobalt phosphide and amorphous cobalt hydroxide are loaded, and the amorphous cobalt hydroxide is distributed on the surface or interface of the crystalline cobalt phosphide. The preparation method includes the following steps: S1, dissolving cobalt salt, urea and ammonium fluoride in water to obtain a mixed solution, placing pretreated carbon in the mixed solution, performing a hydrothermal reaction, and then removing the carbon cloth to obtain a carbon cloth-loaded phosphating precursor; S2, subjecting the carbon cloth-loaded phosphating precursor to phosphating with a phosphorus source under a protective atmosphere to obtain carbon cloth-loaded cobalt phosphide; S3, using the carbon cloth-loaded cobalt phosphide as the working electrode and cobalt salt as the electrolyte, performing constant voltage electrodeposition to obtain the cobalt-based phosphide nanocatalyst material.

2. The method for preparing a cobalt-based phosphide nanocatalytic material according to claim 1, characterized in that, In S1, the carbon cloth pretreatment includes the following steps: placing the carbon cloth in nitric acid and reacting it at 120-160℃ for 6-12 hours.

3. The method for preparing a cobalt-based phosphide nanocatalytic material according to claim 1, characterized in that, In S1, the cobalt salt is cobalt nitrate hexahydrate or cobalt chloride; the molar ratio of cobalt salt, urea and ammonium fluoride is 2:(4.5-5.5):(9.0-11.0).

4. The method for preparing a cobalt-based phosphide nanocatalytic material according to claim 1, characterized in that, In S1, the hydrothermal reaction temperature is 120-160℃ and the time is 6-10h.

5. The method for preparing a cobalt-based phosphide nanocatalytic material according to claim 1, characterized in that, In S2, the phosphorus source is sodium hypophosphite or potassium hypophosphite, and 1.0-2.0 g of phosphorus source is added to every six square centimeters of carbon cloth.

6. The method for preparing a cobalt-based phosphide nanocatalytic material according to claim 1, characterized in that, In S2, the process parameters for the phosphating treatment include at least one of the following: heating rate of 1-3℃ / min; phosphating temperature of 320-380℃; and holding time of 1.5-3h.

7. The method for preparing a cobalt-based phosphide nanocatalytic material according to claim 1, characterized in that, In S3, the cobalt salt is cobalt nitrate hexahydrate or cobalt chloride; the concentration of the cobalt salt is 0.1 mol / L.

8. The method for preparing a cobalt-based phosphide nanocatalytic material according to claim 1, characterized in that, In S3, during constant voltage electrodeposition, a carbon rod is used as the counter electrode and a silver chloride electrode is used as the reference electrode. The process parameters for constant voltage electrodeposition include: cathode voltage of -0.8V to -1.2V and time of 600-1200s.

9. A cobalt-based phosphide nanocatalytic material, characterized in that, The substrate is made of carbon cloth, on which crystalline cobalt phosphide and amorphous cobalt hydroxide are loaded, and the amorphous cobalt hydroxide is distributed in the form of nano-islands on the surface or interface of crystalline cobalt phosphide; or it is prepared by any one of the preparation methods described in claims 1-8.

10. The application of the cobalt-based phosphide nanocatalyst as described in claim 9 as an electrocatalyst in the hydrogen evolution reaction and oxygen evolution reaction.

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